XBD-1and PT-1 scheelites: potential reference materials for SIMS oxygen isotope analysis

Abstract

Scheelite is a common accessory mineral and an essential component of tungsten ores. Its U-Pb dating, chemical compositions, and oxygen isotopes provide critical information on the timing and genesis of scheelite-bearing ores, as well as the nature and evolution of the ore-forming fluids. In situ analysis by secondary ion mass spectrometry (SIMS) is only option for oxygen isotope investigation of natural scheelite crystals, as they commonly exhibit complex growth zoning and contain inclusions. However, there is a current lack of well-characterized scheelite reference materials for SIMS oxygen isotope analysis. This study thus characterizes two natural scheelite samples (XBD-1 and PT-1) as working reference materials for in situ oxygen isotopic analysis of this mineral employing secondary ion mass spectrometry (SIMS). Our SIMS analyses reveal that both XBD-1 and PT-1 scheelite samples exhibit homogeneous oxygen isotopic compositions with their 1SD being 0.2‰ (n=117), and 0.3‰ (n=101), respectively, supporting their use as reference materials for high-precision SIMS δ18O analysis of scheelite. Laser fluorination isotopic ratio mass spectrometry yields mean δ¹⁸O values of 8.57 ± 0.20‰ (1SD, n = 2) for XBD-1 and −6.21 ± 0.20‰ (1SD, n = 3) for PT-1, which are recommended as reference oxygen isotopic values of these materials.